This is, perhaps, the trival final piece of #7075 that I've been
working on.

There's more work to be done: 
- push more of the setup into the pacakges themselves
- move channel-based sending/filtering out of the 
- simplify the buffering throuhgout the p2p stack.

A fourth #7075 component patch to simplify the channel creation interface

This is another small sliver of #7075, with the intention of removing
the legacy shim layer related to channel registration.

Remove v0 blocksync folder structure.

This PR adds an initial set of metrics for use ABCI. The initial metrics enable the calculation of timing histograms and call counts for each of the ABCI methods. The metrics are also labeled as either 'sync' or 'async' to determine if the method call was performed using ABCI's `*Async` methods.

An example of these metrics is included here for reference:
```
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="0.0001"} 0
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="0.0004"} 5
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="0.002"} 12
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="0.009"} 13
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="0.02"} 13
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="0.1"} 13
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="0.65"} 13
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="2"} 13
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="6"} 13
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="25"} 13
tendermint_abci_connection_method_timing_bucket{chain_id="ci",method="commit",type="sync",le="+Inf"} 13
tendermint_abci_connection_method_timing_sum{chain_id="ci",method="commit",type="sync"} 0.007802058000000001
tendermint_abci_connection_method_timing_count{chain_id="ci",method="commit",type="sync"} 13
```

These metrics can easily be graphed using prometheus's `histogram_quantile(...)` method to pick out a particular quantile to graph or examine. I chose buckets that were somewhat of an estimate of expected range of times for ABCI operations. They start at .0001 seconds and range to 25 seconds. The hope is that this range captures enough possible times to be useful for us and operators.

This commit should be one of the first to land as part of the v0.36
cycle *after* cutting the 0.35 branch. 

The blocksync/v2 reactor was originally implemented as an experiement
to produce an implementation of the blockstack protocol that would be
easier to test and validate, but it was never appropriately
operationalized and this implementation was never fully debugged. When
the p2p layer was refactored as part of the 0.35 cycle, the v2
implementation was not refactored and it was left in the codebase but
not removed. This commit just removes all references to it.

When shutting down blocksync, it is observed that the process can hang completely. A dump of running goroutines reveals that this is due to goroutines not listening on the correct shutdown signal. Namely, the `poolRoutine` goroutine does not wait on `pool.Quit`. The `poolRoutine` does not receive any other shutdown signal during `OnStop` becuase it must stop before the `r.closeCh` is closed. Currently the `poolRoutine` listens in the `closeCh` which will not close until the `poolRoutine` stops and calls `poolWG.Done()`.

This change also puts the `requestRoutine()` in the `OnStart` method to make it more visible since it does not rely on anything that is spawned in the `poolRoutine`.

```
goroutine 183 [semacquire]:
sync.runtime_Semacquire(0xc0000d3bd8)
        runtime/sema.go:56 +0x45
sync.(*WaitGroup).Wait(0xc0000d3bd0)
        sync/waitgroup.go:130 +0x65
github.com/tendermint/tendermint/internal/blocksync/v0.(*Reactor).OnStop(0xc0000d3a00)
        github.com/tendermint/tendermint/internal/blocksync/v0/reactor.go:193 +0x47
github.com/tendermint/tendermint/libs/service.(*BaseService).Stop(0xc0000d3a00, 0x0, 0x0)
        github.com/tendermint/tendermint/libs/service/service.go:171 +0x323
github.com/tendermint/tendermint/node.(*nodeImpl).OnStop(0xc00052c000)
        github.com/tendermint/tendermint/node/node.go:758 +0xc62
github.com/tendermint/tendermint/libs/service.(*BaseService).Stop(0xc00052c000, 0x0, 0x0)
        github.com/tendermint/tendermint/libs/service/service.go:171 +0x323
github.com/tendermint/tendermint/cmd/tendermint/commands.NewRunNodeCmd.func1.1()
        github.com/tendermint/tendermint/cmd/tendermint/commands/run_node.go:143 +0x62
github.com/tendermint/tendermint/libs/os.TrapSignal.func1(0xc000df6d20, 0x7f04a68da900, 0xc0004a8930, 0xc0005a72d8)
        github.com/tendermint/tendermint/libs/os/os.go:26 +0x102
created by github.com/tendermint/tendermint/libs/os.TrapSignal
        github.com/tendermint/tendermint/libs/os/os.go:22 +0xe6


goroutine 161 [select]:
github.com/tendermint/tendermint/internal/blocksync/v0.(*Reactor).poolRoutine(0xc0000d3a00, 0x0)
        github.com/tendermint/tendermint/internal/blocksync/v0/reactor.go:464 +0x2b3
created by github.com/tendermint/tendermint/internal/blocksync/v0.(*Reactor).OnStart
        github.com/tendermint/tendermint/internal/blocksync/v0/reactor.go:174 +0xf1

goroutine 162 [select]:
github.com/tendermint/tendermint/internal/blocksync/v0.(*Reactor).processBlockSyncCh(0xc0000d3a00)
        github.com/tendermint/tendermint/internal/blocksync/v0/reactor.go:310 +0x151
created by github.com/tendermint/tendermint/internal/blocksync/v0.(*Reactor).OnStart
        github.com/tendermint/tendermint/internal/blocksync/v0/reactor.go:177 +0x54

goroutine 163 [select]:
github.com/tendermint/tendermint/internal/blocksync/v0.(*Reactor).processPeerUpdates(0xc0000d3a00)
        github.com/tendermint/tendermint/internal/blocksync/v0/reactor.go:363 +0x12b
created by github.com/tendermint/tendermint/internal/blocksync/v0.(*Reactor).OnStart
        github.com/tendermint/tendermint/internal/blocksync/v0/reactor.go:178 +0x76
```

The code in the Tendermint repository makes heavy use of import aliasing.
This is made necessary by our extensive reuse of common base package names, and
by repetition of similar names across different subdirectories.

Unfortunately we have not been very consistent about which packages we alias in
various circumstances, and the aliases we use vary. In the spirit of the advice
in the style guide and https://github.com/golang/go/wiki/CodeReviewComments#imports,
his change makes an effort to clean up and normalize import aliasing.

This change makes no API or behavioral changes. It is a pure cleanup intended
o help make the code more readable to developers (including myself) trying to
understand what is being imported where.

Only unexported names have been modified, and the changes were generated and
applied mechanically with gofmt -r and comby, respecting the lexical and
syntactic rules of Go.  Even so, I did not fix every inconsistency. Where the
changes would be too disruptive, I left it alone.

The principles I followed in this cleanup are:

- Remove aliases that restate the package name.
- Remove aliases where the base package name is unambiguous.
- Move overly-terse abbreviations from the import to the usage site.
- Fix lexical issues (remove underscores, remove capitalization).
- Fix import groupings to more closely match the style guide.
- Group blank (side-effecting) imports and ensure they are commented.
- Add aliases to multiple imports with the same base package name.